1. Field
The present disclosure generally relates to the fabrication composite structures, and deals more particularly with a method and apparatus for producing fillers used to fill gaps in such structures.
2. Background
Composite structures may be fabricated by joining two or more members together. In some cases, there may be one or more gaps in areas of joints between the members that may reduce the strength of the joints. In order to strengthen the joints, the gaps are filled with fillers, sometimes also referred to as radius fillers, fillets or noodles. The filler may be formed from composite materials such as adhesive, prepreg tape or fabric. In some cases, the cross section of the gap may vary in size and/or shape along its length as a result of the adjoining composite members converging or diverging from each other. For example, ply pad-ups, ply drop-offs and/or joggles on a composite skin may result in a variable gap between the skin and an overlying stiffener, such as a stringer, that is attached to the skin.
In the past, fillers having variable cross sectional shapes were fabricated using hand layup techniques that involved laminating unidirectional fiber prepreg tape, in which the fiber orientation was parallel to the length of the gap. This hand layup technique required multiple processing steps, was labor intensive and time consuming. Additionally, fillers employing unidirectional fiber reinforcement may be subject to movement and may not exhibit the desired degree of resistance to cracking.
Accordingly, there is a need for a method and apparatus for producing a composite filler having a variable cross section along its length, that are reliable and repeatable, and which reduce labor costs by automating the fabrication process. There is also a need for a method and apparatus as described above which result in a filler having improved stiffness, toughness and/or resistance to cracking.